Longitudinal Protection Method Based on Voltage Wave Comparison in AC/DC Hybrid System

Abstract

When a fault occurs on the tie line of ac/dc hybrid system, the change rule of electrical quantity on the inverter side is different from that of infinite ac power source. Sensitivity and reliability of the traditional relay protection methods will be affected. A longitudinal protection method for ac/dc hybrid system based on voltage wave similarity comparison is proposed. The protection compares the similarity of the measuring voltage wave and the calculated reference voltage wave, and determines the fault location roughly. By comparing the judgment results of voltage similarity between both ends of line, a reliable judgment can be made to distinguish between internal and external faults. In order to improve the reliability of voltage wave similarity comparison, dynamic time warping method is used to overcome the influence caused by phase error, and Pearson correlation coefficient method is used to judge the similarity of voltage wave. The simulation results of real time digital simulation system (RTDS) show that the proposed method can identify the fault which occurs on the tie line of ac/dc hybrid system accurately which has high reliability and good applicability.